Samplers of this kind are described, for example, in DE-U 297 22 468, DE-A 102 52 158, DE-A 28 24 153, WO-A 95/02176 and U.S. Pat. No. 4,415,011 and are available from the assignee under the names LIQUI-PORT and LIQUI-BOX. Especially the sampler described in DE-U 297 22 468 is also provided for application in an explosion-endangered area.
Special safety requirements are placed on devices usable in explosion-endangered areas. These requirements have the goal of avoiding the creation of sparks, which, under the right conditions, could trigger an explosion, or of preventing that a spark occurring inside a closed space results in effects on the surroundings. This goal is achievable in various ways referenced in corresponding European standards as ignition protection types. Thus, e.g., according to European Standard EN 50 020 dated 1994, explosion protection is present, when devices are constructed according to the protection class defined therein with the name ‘Intrinsic Safety’ (EEx ‘ib’). According to this protection class, the values for the electrical variables current, voltage, converted, respectively convertible, power, and stored or storable energy in a device must lie, at all times, below specified limit values. The limit values are selected such that, in case of a malfunction, e.g. a short circuit, the maximum resulting heat is not sufficient to produce an ignition spark. The current is e.g. held within specified limit values by resistances, the voltages e.g. by Zener diodes, and the power by corresponding combinations of current and voltage limiting components. The European Standard EN 50 019 dated 1994 specifies a further protection class with the name “Extended Safety” (EEx ‘e’). In the case of devices, which are constructed according to this protection class, the explosion protection is achieved by providing spatial separations between two different electric potentials sufficiently great that a spark formation is prevented by distance in the case of malfunction. This can, however, lead in certain circumstances to the necessity for very large dimensions, in order to satisfy these conditions. A further protection class bearing the designation “Pressure-Tight Encapsulation” (EEx ‘d’) is described in the European Standard EN 50 018 dated 1994. Devices which are constructed according to this protection class have a pressure-tight housing, which assures that an explosion occurring in the interior of the housing cannot be transmitted to the exterior. Pressure-tight housings are thick-walled, in order to have a sufficient mechanical strength, and are consequently heavy and expensive. The USA, Canada, Japan and other countries have standards which are comparable with these European standards.
The sampler described in DE-U 297 22 468 is, for the purpose of assuring a sufficient explosion safety, provided with an explosion protection device supplied by an auxiliary, current and compressed air supply, with practically all electrical components of the sampler being accommodated in the single, explosion-secured housing. However, a disadvantage of this explosion protection device can be seen in that this current and compressed air supply can itself potentially fail, in which case, in turn, the explosion protection for the entire sampler is terminated unexpectedly and suddenly. A further disadvantage of this sampler is that the auxiliary current and compressed air supply also effects a considerable increase in the weight of the sampler, which, in turn, degrades portability considerably.